How do you calculate the square root of a negative number

Yes anon is right.

There are no real solutions to the square root of a negative number.

Any real number multiplied by itself must give a positive answer!

However there is another whole number system full of 'imaginary numbers'

The basic unit for imaginary numbers is   $$\sqrt{-1}$$     which is called   $$i$$     (or sometimes j)

so

if   $$a$$    is a positive number then     $$\sqrt{-a}=\sqrt{-1}\times\sqrt{a} = i\sqrt{a}$$

 ⇶ How do you calculate the square root of a negative number?

You calculate the square root of the positive number, then write i in front of it because i is a symbol for $${\sqrt{-{\mathtt{1}}}}$$